1. Field of the Invention
The present invention relates to a synthetic peptide that increases the radiosensitivity of tumor cells and to the use thereof. More particularly, the present invention relates to a pharmaceutical composition containing this synthetic peptide and the use of that pharmaceutical composition.
The present application claims priority on the basis of Japanese Patent Application No. 2015-110910, filed on May 29, 2015, the entire contents of which are incorporated herein by reference.
2. Description of the Related Art
Typical examples of methods used to treat tumors (and typically, malignant tumors or cancer) include surgical treatment, radiation therapy and chemotherapy. The methods used to treat these tumors (and typically, malignant tumors) are typically classified into local treatment, in which the site of tumor formation is treated locally, and systemic treatment, which targets the entire body of the patient (cancer patient) for treatment. Surgical treatment and radiation therapy are typical examples of local treatment for tumors, while chemotherapy is a typical example of systemic treatment for tumors.
Radiation therapy allows a tumor to be treated without surgery (resection). In addition, treating a tumor by combining surgical treatment and radiation therapy makes it possible to narrow the range of surgical resection in comparison with the case of treating the tumor by surgical treatment only. Namely, physical invasion accompanying surgical treatment (surgery) can be reduced by selecting radiation therapy (including cases of using in combination with surgical treatment). In addition, since it is also possible to preserve the organ where the tumor has formed (morphological preservation and functional preservation) as well as maintain aesthetics, it is highly useful to select radiation therapy (including cases of using in combination with surgical treatment).
In addition, radiation therapy is also characterized by enabling sites to be treated where surgery is difficult (i.e. it is possible to irradiate the site with radiation) and typically has less effect (adverse side effects) on the body in comparison with chemotherapy.
Radiation therapy refers to a method for controlling a tumor by utilizing the actions of radiation that inhibit cell growth and cause cell death. Since sensitivity to and reactivity with radiation differs between tumor cells and normal cells, cell proliferation by tumor cells can be inhibited and tumor cells can be caused to die by utilizing these differences in sensitivity and reactivity.
DNA can typically be damaged (cleaved) in cells irradiated with radiation. This is because cells in which DNA has been damaged tend to have difficulty in undergoing normal cell division. Namely, cell proliferation is inhibited as a result of cells dying due to being unable to carry out cell division or undergoing incomplete cell division, for example. In addition, cells in which DNA have been damaged may also die as a result of the DNA damage inducing apoptosis.
The Bergonie-Tribondeau law of radiosensitivity is known regarding sensitivity of cells to radiation, and in other words, states that the sensitivity to radiation of a cell increases as the frequency of cell division becomes higher, that sensitivity to radiation of a cell increases as the number of times that cell undergoes division in the future becomes higher, and that more morphologically and functionally undifferentiated cells exhibit higher sensitivity to radiation. In general, since there are many cases in which tumor cells match these characteristics in comparison with normal cells, they are more susceptible to the effects of radiation. In addition, tumor cells typically have a poorer function for repairing DNA damage caused by exposure to irradiation in comparison with normal cells. Thus, irradiating a tumor formation site with radiation makes it possible to inhibit the proliferation of tumor cells constituting the tumor and cause the tumor cells to die while minimizing the effects on normal cells present around the tumor.